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Conversion of oils into esters and glycerol (or other glycerol‐free products) must be energy and cost efficient while being fairly controllable and adaptable with different oils. Transesterification (occasionally coupled with esterification) is the most widely sought approach because of its simplicity combined with versatility [6]. Mostly in conventional transesterification approaches, the use of catalysts is also an important factor both chemically (saving energy) and economically (reusability of heterogeneous catalysts compared with high reagent use in homogeneous systems). Catalyst preparation and/or use comes with added costs. It had been earlier established by Karmakar et al. [3] that feedstock procurement and refining can comprise up to 70% of the fuel price, and this goes up when uncommon nonedible oils are used, due to collection and processing. A simple way to overcome this is through the use of WCO, which are commonly available and can drastically cut down production costs [12]. Using waste biomass for catalyst synthesis is another step toward cost efficiency; however, that lies beyond the scope of the presented discussion.

In frying, the oils are used for multiple rounds (usually 8–10), and the process of reheating the oils past its smoke point results in thermal degradation of the glycerides and fatty acids, burning as well as inducing rancidity. The oils thus turn bitter and become unfit for further use, at which point they are discarded. Although small in quantity for each food outlet, the global scenario is quite insurmountable. According to the American Petroleum Institute, about 63.5 million barrels of WCO are discarded annually, whereas the average household needs only 0.063 barrels of this oil to produce enough electricity for a day [13]. Animal fats also contain very high amounts of free fatty acids (FFAs) and water, and thus cannot be transesterified without proper pretreatment [14].